Flexible thermoplastic pouches or containers are commonly used to package a wide variety of articles and products such as foodstuffs, beverages, medical instruments, and medical solutions. Thermoplastic sheet material is used in making such pouches because it exhibits good moisture barrier properties and is relatively easy to shape, form, fill, and seal.
Virtually all thermoplastic sheet material that is used in making flexible pouches or containers, whether blown, rolled, cast or die extruded, is directionally oriented to some degree. In addition, some thermoplastic sheet material is intentionally oriented by stretching either longitudinally, transversely, or both. Accordingly, it is relatively easy to open a thermoplastic pouch by tearing the thermoplastic sheet material in the direction of orientation. However, it is much more difficult to tear thermoplastic sheet material along a line that is transverse, angled, or curved relative to the material's orientation direction. Of course, one way of opening a thermoplastic pouch along a predetermined line is to use an implement such as a knife or scissors. However, such implements never seem to be readily available when needed, or must be sterile if the pouch and its contents are to remain in a sterile condition in those applications where sterility is essential, e.g., an operating room during a surgical procedure.
One known method of opening a thermoplastic pouch without using an implement is to tear the pouch along a score line or line of weakness that has been provided in the area where the pouch is intended to be opened. However, a score line is not entirely satisfactory because it weakens the pouch, thereby making it more likely to accidentally rupture along the line during transport and handling. In addition, the thermoplastic material is considerably thinner in the area of the score line, which severely detracts from the material's gas and moisture barrier properties.
One proposed alternative to using a score line or line of weakness to open a thermoplastic pouch is to provide the pouch with an opening that is covered with a patch or tear strip, an example of which is disclosed in U.S. Pat. No. 2,991,000 to Spees. As disclosed, an elongated hole or slot is first cut in one of the pouch's sidewalls, followed by covering the slot with a strip of thermoplastic material on the sidewall's interior surface, and a tear seal member on the sidewall's exterior surface. To open the pouch, the tear seal member is pulled away from the slot, which also tears away the portion of the interior strip covering the slot. While this type of "patch" system does provide a relatively easy way to open a thermoplastic pouch, the system has some serious drawbacks. First, the method of making such a pouch is relatively slow given the number of individual steps which must be performed. Second, handling, precisely registering, and sealing small individual strips of plastic material to a thermoplastic sheet is difficult, particularly in a high-speed manufacturing environment. Finally, it is difficult to obtain a reliable, liquid-tight seal between the slot and the patch.
One tear strip means for opening a thermoplastic pouch that is believed to be far superior to the Spees tear strip is disclosed in commonly assigned U.S. Pat. No. 4,496,046 to Stone et al., which is hereby incorporated herein by reference. In FIGS. 4 through 6 of Stone, there is illustrated a thermoplastic pouch having an easy-open tear strip sealed to one of the pouch's sidewalls. In direct contrast to Spees, Stone's tear strip does not cover a slot or opening in the pouch's sidewall; rather, a slot is created when the tear strip is pulled away from the pouch. Therefore, since the pouch is not initially provided with a slot that must be subsequently "patched," the pouch's moisture barrier and liquid containing capacity is greatly enhanced. In addition, the seal between the tear strip and the pouch does not have to be liquid-tight, which allows high-speed manufacturing parameters and tolerances to be much less critical than when a liquid-tight seal is required.
Despite the above-discussed advantages of the Stone tear strip and commercial success thereof, it has been found that it is sometimes difficult to initiate the separation of the tear strip from the pouch. In addition, the tear strip does not always separate from the pouch along the intended path, thereby resulting in an opening having an irregular and random shape. As expected, once the tear veers off course, it is difficult if not impossible for the operator to direct the tear back on track. It is believed that the plastic material's earlier-discussed orientation characteristics combined with an increased amount of plastic material in the area of the securement lines between the pouch and tear strip may be the primary causes of these problems.
In light of the above, a principal object of the present invention is to provide a flexible, thermoplastic pouch with easy-open tear strip means for opening the pouch, thereby eliminating the need to use an implement such as a knife or scissor.
Another principal object of the present invention is to provide a flexible, thermoplastic container with easy-open tear strip means without requiring an aperture or slot to be punched in the pouch's sidewall before the strip is applied thereto.
Another principal object of the present invention is to provide a thermoplastic pouch with tear strip means that will easily and readily separate from the pouch.
A further object of the present invention is to provide a thermoplastic pouch with an easy-open tear strip that will repeatedly separate from the pouch along a predetermined path to thereby create a dispensing opening of predetermined size and shape.
Another object of the present invention is to provide a thermoplastic pouch with an easy-open tear strip that will not reduce the pouch's strength, gas and moisture barrier properties, or liquid containing ability prior to opening.
A further object of the present invention is to provide a sealing die apparatus for attaching tear strip means to a flexible, thermoplastic pouch.